Heavy Snow in Alaska, February 21 to 22, 2007

SOUTHEAST ALASKA FORECAST DISCUSSION
1100 AM AST WED FEB 21 2007

.SYNOPSIS...
.SHORT RANGE...SATELLITE IMAGERY THIS MORNING REVEALS A LOW IN
THE NORTHEAST GULF THAT IS SLOWLY TRACKING SOUTHEAST TOWARDS THE
SOUTHERN PANHANDLE. ON THE EAST SIDE OF THIS LOW...BANDS OF
CLOUDS AND SHOWERS ARE TRACKING NORTH AND INTENSIFYING AS THEY
MOVE OVER THE PANHANDLE. CURRENTLY RAIN IS LIMITED TO THE
SOUTHERN PORTIONS OF ZONE 28 WITH SNOW AND SNOW SHOWERS
ELSEWHERE. AN UPPER LEVEL LOW LOCATED OVER NORTHERN YUKON MOVES
SOUTH ALONG THE ALASKA YUKON BORDER AND DEEPENS SLIGHTLY
THROUGHOUT THE SHORT TERM FORECAST PERIOD. THE ASSOCIATED UPPER
LEVEL TROUGH CURRENTLY EXTENDS INTO THE GULF ABOVE THE SURFACE
LOW. THIS DIGGING TROUGH COMBINED WITH UPWARD VERTICAL MOTION
NEAR THE SURFACE LOW AND MOIST ONSHORE SOUTHERLY FLOW WILL
ENHANCE SNOW SHOWER ACTIVITY FOR THE NEXT DAY OR
TWO...PARTICULARLY IN THE CENTRAL PANHANDLE. AM EXPECTING SNOW
SHOWERS TO INCREASE THROUGHOUT THE DAY TODAY WITH THE HEAVIEST
SNOW INITIALLY IN ZONE 26 AND MOVING NORTH AS A WARM FRONT THIS
EVENING OVER THE TOP OF THE COLD SURFACE SURFACE AIR ESTABLISHED
OVER THE PANHANDLE. SNOW AMOUNTS WILL TAPER OFF NORTH OF ICY
STRAIT AS MID LEVEL MOISTURE AMOUNTS DECREASE THROUGH THE NIGHT.
CURRENT HEAVY SNOW WARNINGS AND SNOW ADVISORIES LOOK TO BE ON
TRACK RIGHT NOW AND WILL UPDATE WITH THE AFTERNOON FORECAST.

THE NORTHERLY PRESSURE GRADIENT REMAINS IN PLACE OVER THE
NORTHERN ZONES AND IS NOT EXPECTED TO RELAX DURING THE SHORT TERM
FORECAST PERIOD AS ANOTHER SURFACE LOW FORMS IN THE EXTREME
NORTHEAST GULF BY THURSDAY AFTERNOON. ASSOCIATED COLD AIR WILL
RESULT IN CONTINUED WIND CHILL ADVISORIES FOR THE NORTHERN ZONES
AND FREEZING SPRAY WARNINGS FOR THE NORTHERN INNER CHANNELS.

.LONG RANGE...OVERALL...NOT TOO MANY CHANGES EXPECTED IN THE
UPCOMING FORECAST PACKAGE. THERE APPEARS TO BE REASONABLE RUN TO
RUN CONSISTENCY WITH THE MODEL FORECASTS. SURFACE BOUNDARY IS
EXPECTED TO REMAIN NEARLY STATIONARY ACROSS THE SOUTHERN PART OF
THE PANHANDLE AS SEVERAL WAVES DEVELOP ALONG THE FRONT AND MOVE
INLAND.

LARGER SCALE LOW IS FORECAST TO MOVE INTO THE SOUTHWESTERN GULF
OF ALASKA DURING THE DAY TOMORROW AND WILL TAKE A LITTLE MORE
SOUTHERN TRACK AS IT MOVES ACROSS THE GULF. AS IT APPROACHES THE
SOUTHERN PANHANDLE...IT MAY HELP TO FORCE THE QUASISTATIONARY
BOUNDARY FARTHER NORTH ACROSS THE PANHANDLE. MOISTENING OF THE
LOW LEVELS WILL BE SOMEWHAT SLOW TO OCCUR GIVEN THAT THE AIR HAS
BEEN SIGNIFICANTLY DRIED OUT DUE TO THE ARCTIC NATURE OF THE
AIRMASS THAT IS IN PLACE. THEREFORE...THE HIGHEST POPS WILL BE
ACROSS THE SOUTHERN PANHANDLE WHERE SUFFICIENT AIRMASS
MODIFICATION WILL HAVE TAKEN PLACE.

AS THIS SURFACE LOW SHIFTS SOUTH ON SUNDAY...THE ARCTIC FRONT
WILL AGAIN SAG SOUTHWARD ACROSS THE CENTRAL AND SOUTHERN
PANHANDLE.

WINDS ACROSS THE NORTHERN PART OF THE AREA WILL REMAIN A CONCERN
GIVEN THAT A TIGHT PRESSURE GRADIENT WILL REMAIN IN PLACE. THERE
WILL BE A LOOSENING OF THE GRADIENT DURING THE FIRST PART OF NEXT
WEEK...BUT ANOTHER LOW WILL BE MOVING INTO THE NORTHEAST GULF
BEGINNING TUESDAY WHICH WILL RE-TIGHTEN THE GRADIENT AND THE
ACCOMPANYING WINDS. THIS SHOULD CONTINUE INTO THE MIDDLE OF NEXT
WEEK.

.AJK...WATCHES/WARNINGS/ADVISORIES
PUBLIC...HEAVY SNOW WARNING...AKZ24 AND 26
         SNOW ADVISORY...AK21 AND 25
         WIND ADVISORY...AKZ17-19
         WIND CHILL ADVISORY...AKZ18 ALONG THE KLONDIKE HIGHWAY
MARINE...GALE...PKZ51...21-22...11-13
         SCA...PKZ52...41-43...31...32...34
         HEAVY FREEZING SPRAY...PKZ11-13 THROUGH THURSDAY